Mobile phones, personal digital assistants (“PDAs”), digital cameras, MP3 players, and other portable electronic devices utilize SSL devices (e.g., light emitting diodes (LEDs)) for background illumination. SSL devices are also used for signage, indoor lighting, outdoor lighting, and other types of general illumination. FIGS. 1A and 1B are cross-sectional and plan views, respectively, of a conventional SSL device 10. As shown in FIGS. 1A and 1B, the SSL device 10 includes a substrate 12 carrying an LED structure 11 having N-type gallium nitride (GaN) 14, GaN/indium gallium nitride (InGaN) multiple quantum wells (“MQWs”) 16, and P-type GaN 18. The SSL device 10 also includes a first terminal 20 in contact with the N-type GaN 14 and a second terminal 22 in contact with the P-type GaN 18. The first terminal 20 includes a plurality of contact fingers 21 (three are shown for illustration purposes) coupled to one another by a cross member 23. The second terminal 22 includes a sheet-like structure.
In operation, a continuous or pulsed electrical voltage is applied between the first and second terminals 20 and 22. In response, an electrical current flows from the first terminal 20, through the N-type GaN 14, the GaN/InGaN MQWs 16, and the P-type GaN 18, to the second terminal 22. The GaN/InGaN MQWs 16 then convert a portion of the electrical energy into light. The generated light is extracted from the N-type GaN 14 of the SSL devices 10 for illumination, signage, and/or other suitable purposes.
The SSL device 10, however, may have low light extraction efficiencies. According to conventional techniques, the first and second terminals 20 and 22 typically include aluminum, copper, or other nontransparent conductive materials. As a result, light generated in areas directly between the first and second contacts 20 and 22 can be difficult to extract. On the other hand, the areas directly between the first and second contacts 20 and 22 produce the highest intensity of light in the SSL device 10. As a result, a large portion of the light generated in the SSL device 10 may not be extracted, which results in low light extraction efficiencies. Accordingly, several improvements in increasing light extraction efficiency in SSL devices may be desirable.